A bead is a small, decorative object that is usually pierced for threading or stringing. Beads range in size from under 1 millimetre (0.039 in) to over 1 centimetre (0.39 in) in diameter. A pair of beads made from Nassarius sea snail shells, approximately 100,000 years old, are thought to be the earliest known examples of jewellery. Beads may be divided into several types of overlapping categories, based on different criteria such as component materials, manufacturing process, place or period of origin, surface patterning, or general shape. In some cases, such as millefiori and cloisonné beads, multiple categories may overlap in an inseparably interdependent fashion

Beads can be made of many types of materials. The earliest beads were made of convenient natural materials; when found, these could be readily drilled and shaped. As human technology became capable of obtaining or working with more difficult natural materials, those were added to the range of available substances. The same was true of new synthetic materials when created.

Beads are still made from many naturally-occurring materials, both organic (i.e., of animal- or plant-based origin) and inorganic (purely mineral origin). However, some of these materials now routinely undergo some extra human processing beyond mere shaping and drilling, such as color enhancement via dyes or irradiation. For most of human history, pearls were the ultimate precious beads of natural origin because of their rarity, although the pearl-culturing process has now made them far more common. Amber and jet are also of natural organic origin, although both materials have undergone partial geologic fossilization.